The introduction of the surface mounting technique (SMT) makes it possible to put a large number of components on a circuit board, which is necessary partly because of the recent progress in the field of miniaturization and the improved performance of various apparatuses, and partly to ensure a further improvement in productivity. In the older techniques used for soldering components on a printed circuit board, pins attached to the components are pushed through holes in the circuit board. The ends of the pins are then brought into contact with a liquid solder, so that they become fixed in their position after cooling. In this method, the components themselves are not exposed to the high temperatures involved in the soldering process. In the surface mounting technique, on the other hand, the components are indeed exposed to these high temperatures.
This means that only polymers which have a melting temperature well above the temperature involved in the soldering operation, e.g. above 265.degree. C., can be considered for use. This rules out some conventional plastics such as nylon-6, nylon-6,6, polyethylene terephthalate and polybutylene terephthalate. The problem with high-melting polymers such as polyphenylene sulphide (PPS) and aromatic polyamides, on the other hand, is that their mechanical characteristics or processing properties have certain limitations.
However, polytetramethyleneadipamide, an aliphatic polyamide-4,6 with a melting point of about 290.degree. C., is much better in this respect, for it can be processed even if it has a very small wall thickness, and it exhibits good mechanical properties. No problems are encountered when electrical and electronic components made of this polyamide-4,6 are incorporated in circuits directly after production, i.e. in the "dry-as-moulded" state, with the aid of the surface mounting technique.
However, blisters can form on the polyamide component in a number of cases during soldering with the surface mounting technique if the polyamide component has been in contact with atmospheric air for a fairly long time so that it has absorbed some moisture from it, especially under tropical conditions. This is attributed to the high moisture absorption capacity of nylon-4,6, in turn caused by the large number of amide groups in the polyamide. To improve the situation, various attempts have been made to introduce a degree of hydrophobic character by admixing a polyphenylene sulphide or an aromatic polyester (see JP-A-3-263,461, JP-A-4-292,655 and JP-A-5-239,344). However, although this reduces the moisture uptake, it does not completely suppress the blister formation and it has an adverse effect on the mechanical and processing characteristics of the material.